The present invention relates to a contact bus bar assembly for supplying power to a load, and further pertains to a switching device which can be connected to such a compact bus bar assembly. In particular, the present invention relates to a power distribution system using bus bars for conducting higher currents, e.g. when supplying power to a motor and wherein switching devices are used, for instance, for opening and closing the connection to the power supply.
For instance, from U.S. Pat. No. 7,084,727 B2, such switching devices are known which have separating elements between terminals of different polarity that are provided on an adapter element. The disadvantage of this arrangement can be seen firstly in the fact that the footprint is much larger than the size of the switching device according to the present invention. Secondly, the electrically insulating elements are only provided on adapter units which are independent of the standard switch unit. Thus, the dimension in a direction across the bus bar assembly is rather large, which for instance in connection with switching cabinets is disadvantageous.
In particular, in the field of circuit breakers for switching off loads, often high currents occur and particular requirements regarding creepage distances and air gaps have to be fulfilled regarding connecting terminals of different polarity.
In particular, electromechanical circuit breakers according to UL 489 (Underwriters Laboratories Inc., UL 489, 11th edition, “Molded Case Circuit Breakers, Molded Case Switches, and Circuit-Breaker Enclosures”, Sep. 1, 2009) require a two inches creepage distance and a one inch clearance distance, which is up to four times larger compared to UL 508 “Manual Motor Controllers” of basically the same design.
In particular, Table 6.1.6.1.1 “Minimum spacings in millimeters” of UL 489 require for voltages of 301 V to 600 V between parts a spacing between terminals of opposite polarity on 25.4 mm through air and 50.8 over surface, respectively.
Furthermore, the corresponding IEC standards do not differentiate these breaker categories and allow dimensions similar to the requirements of UL 508. Consequently, the UL 489 requirements are the most stringent ones and lead normally to considerably larger dimensions and larger footprints (about 30% larger than for UL 508).
One aspect underlying the present invention is therefore to provide a compact bus bar assembly, a switching device and a power distribution system which fulfils the strict requirements according to US 489 and on the other hand is small enough to stay within the footprint of the requirements according to UL 489.